Groundwater Banking: A Likely Solution to Achieve Greater River Flows

A group of volunteers from the Tuolumne River Trust raft down the river near downtown during the Love Modesto event. Ed Crisostomo Modesto Bee

A PROPOSAL BY the California Water Resources Control Board to require additional water to be left in the Tuolumne River and other San Joaquin River tributaries has prompted strong negative opinions, including from some newspapers serving the region, such as the Modesto Bee.

Regrettably, what has received little attention in this debate are the opportunities for improving water management to meet the agricultural and environmental demands placed on these rivers.

A coalition of conservation groups has proposed that Modesto and Turlock irrigation districts, working with the San Francisco Public Utilities Commission, establish a 90,000 acre-foot groundwater bank. Such a partnership has a precedent in the Tuolumne watershed, where San Francisco paid for just over 50 percent of the construction cost of Don Pedro Dam in exchange for the ability to bank up to 570,000 acre-feet in the reservoir.

A groundwater bank could be similarly financed and would be a much more efficient means of protecting groundwater supplies than the current aquifer recharge system, which relies heavily on inefficient flood irrigation. Recharge by flood irrigation requires overapplication of water to agricultural fields. Flood irrigation requires heavy application of water even in dry years and it is unknown how much of the excess water applied actually is recoverable for later use. It also moves nitrates and other pollutants into groundwater, which creates many other problems.

By comparison, an engineered aquifer recharge system would increase efficiency. Such a system would focus on capturing floodwaters during the wettest years, when water is abundant and there are fewer concerns for fish and other species. This system would increase the amount of water that would be usable in future dry years, when there is a greater need for water.

It is a system we believe people on all sides could support.

Another promising tool for water efficiency has been tested in our own backyard. In 2012, the South San Joaquin Irrigation District [SSJID] implemented a cutting-edge project on 3,800 acres of irrigated district lands. In the SSJID, like in its sister districts to the south, water has been delivered through miles of gravity-fed canals, which are inefficient and difficult to manage. In this pilot project, the SSJID converted the canals to 19 miles of pressurized pipeline.

The project reduces water use by 30 percent, reduces energy use by 30 percent and increases crop yield by up to 30 percent. The benefits are clear and should have growers throughout the region demanding that all distribution systems be converted. Assuming similar efficiencies could be achieved by the Modesto Irrigation District and the Tuolumne Irrigation District, this approach could produce about 300,000 acre-feet of conserved water on the Tuolumne alone.

This water would go a long way to meeting the needs of the river and the animals that depend on it and provide benefits to farmers.

Finally, Stanislaus County and the water districts have a responsibility to ensure the region doesn’t pump and divert water beyond its means. The unfettered drilling of new wells, particularly in the eastern foothills, has led to a proliferation of orchards on ground that historically had been grazing land. The annexation of new areas by Oakdale Irrigation District to plant more and more orchards and other permanent crops compounds the problem.

These newcomers to irrigated agriculture are adding stress to an overtapped system and threatening those within the irrigation district boundaries who have been farming for generations. Our water supplies can take no additional demands, and this expansion of cropland must be checked.

While no single strategy will meet water demand, a combination of approaches will help us ensure a healthy agricultural economy, restored rivers and a healthier environment.

Instead of dismissing the water needs of the environment as unachievable, the water districts have an opportunity to lead us successfully into a new era of water management. This is a future that will support a more robust economy, a restored river system and a vibrant quality of life.